The processing time of applying in the store would be enormous there's a reason very few stores still use the price sticker gun to label items, it's time consuming when there's already a tag on each item.
Also in a number of places walmart and other stores literally just open a box provided by their sources and place it on shelves.
Reading a shelf full of products isn't an issue, how do you think they can wave a wand over clothes and know the exact sizes they have and quantity?
They should double down on RFID but many of the manufacturers don't want to incorporate it in their process.